Although nanozyme has shown great potential in designing fluorescent assays for pesticide residue, most of them are based on single emission, thus affecting the detection accuracy. Herein, a copper-based fluorescent nanozyme (Cu-BH) synthesized with dual-ligand, integrating fluorescence and oxidase-mimic into one spherical nanomaterial, was used firstly to establish a ratiometric approach for visual detection of thiophanate methyl (TM). Cu-BH possesses excellent oxidase-like activities, triggering the oxidation of colorless o-phenylenediamine (OPD) into yellow luminescent products (oxOPD, λem = 564 nm). Besides, the ligand of 2-amino-1,4-benzene-dicarboxylic acid imparts Cu-BH blue fluorescence (λem = 425 nm), which is quenched by oxOPD via inner filtration effect (IFE). The introduction of TM can prevent not only the oxidase-like activity remarkably but also the intrinsic luminescence of Cu-BH slightly because of the complexation of TM with Cu2+. As a result, the fluorescence intensity at 564 nm and 425 nm presents a significant decrease and a slight increase, respectively, producing a ratiometric fluorescent signal (F425/F564). Therefore, a novel ratiometric fluorescent strategy has been proposed to detect TM ranging from 0.1 to 100 μM with detection limit of 0.03 μM (S/N = 3). Besides, visual detection of TM can be achieved by RGB reading with the assistance of smartphone owing to the color variation from yellow to blue. This fluorescent nanozyme-based ratiometric strategy provides a specific method for the detection of TM in food samples.
Keywords: Direct nanozyme inhibition; Fluorescent nanozyme; Ratiometric sensors; Thiophanate methyl; Visual detection.
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